Abstract: The impact indentation strain measurement technique, as a new residual stress determination method, is increasingly applied. The calibration method is necessary through strain overlap increment to calculate residual stress. The great error could be produced in measuring the residual stress in a weld with the use of calibration coefficient for the base metal instead of the weld metal. The physical deformation was analyzed firstly, then an improved method to approximately calculate weld stress was put forward. It makes the measuring accuracy of residual stresses raise remarkably.